Polluted Signals: Heavy Metal-Altered Rice Volatiles Mislead Parasitoids and Weaken Natural Pest Control

Abstract

Heavy metal contamination threatens agricultural sustainability, yet its impacts on multitrophic communications remain poorly understood. We investigated how cadmium (Cd) exposure alters rice volatiles and affects host-habitat location in two Trichogramma egg parasitoids. Naïve T. japonicum females were attracted to Cd-exposed rice volatiles, whereas Cd-exposed females avoided them, indicating behavioral plasticity in response to Cd exposure. Trichogramma dendrolimi showed no significant preference regardless of Cd exposure. Gas chromatography–mass spectrometry revealed that Cd stress increased constitutive plant volatiles emissions by 2.94-fold and modified blend compositions, elevating 2-ethylhexanol and cyclohexane carboxylic acid, 2-tetradecyl ester. Behavioral assays identified the latter as a key attractant at low concentrations but repellent to Cd-exposed T. japonicum at high concentrations. Our findings show that Cd pollution can mislead natural enemies and disrupt biological control, with T. dendrolimi showing species-specific resilience that warrants further evaluation. This study provides mechanistic insights for biocontrol strategies in contaminated agricultural landscapes.